The preparation procedure of an array substrate, a color film substrate and the like of a display device such as a liquid crystal display device or an organic light emitting diode display device includes a plurality of different processes. During the processes, in order to store and transport the substrate, it is necessary to place the substrate (which can be in the cassette) on a substrate holder. The substrate holder is a holder having a plurality of layers, each of which has a position for carrying a substrate, and the substrate can be accessed by a robot.
Due to the accumulation of operating errors of the robot, there is a position deviation when the substrate is placed on the substrate holder, and the position deviation may increase with time. When the position deviation of the substrate is increased to a certain extent, the position deviation of the substrate on a base platform of an equipment for processing may be too large, resulting in difficulty in alignment or failure to complete alignment. Or, it may also cause the substrate to touch other structures during transporting, resulting in damage to the substrate.
The relevant substrate holder cannot detect the position of the substrate thereon. In order to avoid excessive deviation of the above substrate position, the relevant method is to measure the position of the substrate on each substrate holder (for example, to measure three substrate holders) periodically (e.g., every quarter) by an artificial sampling measurement, and adjust the robot according to the detection result. Obviously, this method of artificial sampling has problems such as inefficiency, large error, high error rate, not timely and so on.
It should be noted that, information disclosed in the above background portion is provided only for better understanding of the background of the present disclosure, and thus it may contain information that does not form the prior art known by those ordinary skilled in the art.